<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    // let isCool = false
    // let isCool = true
    // console.log(4 > 5);

    // let num
    // console.log(num);

    // let obj = null
    // console.log(obj);

    // console.log(undefined + 1);
    // console.log(null + 1);


  </script>
</body>

</html>